1. Field of the Invention
The present invention relates to a crimp contact, a crimp contact with an electrical lead, a gas sensor provided with said crimp contact and a method for manufacturing said gas sensor including said crimp contact. In particular, the crimp contact includes a hold portion crimping lead core wires of an electrical lead.
2. Description of the Related Art
A conventional type of crimp contact is known to include a hold portion extending axially and holding lead core wires of an electrical lead therein (e.g., Patent Document 1). This hold portion comprises a pair of side portions for fixing the lead core wires by bending front end sides thereof toward the lead core wires of the electrical lead and a bottom portion connecting a rear end side of the pair of side portions.
This crimp contact with an electrical lead is manufactured as follows. First, a crimp contact is prepared. The crimp contact includes a U-shaped hold portion comprising a bottom portion and a pair of side portions rising from both ends of the bottom portion. Further, lead core wires of an electrical lead are disposed so as to be in contact with an inner surface of the U-shaped hold portion. Subsequently, the side portions are bent toward the bottom portion side by a pair of metal molds, i.e., an anvil and a crimper. At this time, the front end sides of the side portions of the U-shaped hold portion slide along a sliding face of the crimper and the side portions are deeply bent into a bundle of the lead core wires of the electrical lead. Then, the front end sides of the side portion are in contact with each other, and the lead core wires are held and crimped by the bottom portion and the side portions.
Incidentally, in the above-mentioned method for manufacturing the crimp contact, a crimping process of the U-shaped hold portion is conducted continuously. Consequently, slidability gradually deteriorates between the outer surfaces of the side portions and the sliding face of the crimper as the metal molds are used repeatedly in the crimping process. When the slidability deteriorates, the front end sides of the side portions insufficiently penetrate the lead core wires, and a crimping height, which is the height of the hold portion, is increased. Thereby, the lead core wires are insecurely fixed in the hold portion. As a result, electrical conductivity between the electrical lead and the crimp contact can deteriorate. In recent years, due to a demand for crimp contact durability and the like, the crimp contact tends to be made of a material having a high degree of Vickers hardness, such as INCONEL (trademark of INCO). Therefore, the slidability between the crimp contact and the crimper tends to deteriorate as the crimper is worn out. Also, the hold portion of the crimp contact tends to adhere to the crimper. Thus, as disclosed in Patent Document 1, a lubricant is applied in advance to the sliding face of the crimper so that slidability may be maintained and the hold portion with an appropriate crimping height can be formed even though the crimping process is performed continuously. As a result, the electrical conductivity between the electrical leads and the crimp contacts can be increased.
Such a crimp contact is assembled in a gas sensor having, for example, a sensor element, a metal housing and a protective cover. Here, the sensor element extends in the axial direction and includes a sensing portion in a front end side thereof. The metal housing is a cylindrical member for holding the sensor element therein so that at least the sensing portion may be exposed from a front end side of the metal housing. The front end side of the protective cover is connected to the rear end side of the metal housing, and the protective cover accommodates therein the electrical leads electrically connected to the external device. The crimp contact electrically connects the sensor element to the electrical lead and is used for outputting a signal from the sensing portion to an external device. The gas sensor is mounted on, for example, an exhaust system of an engine exhaust pipe or the like and used for detecting a gas to be measured (e.g., oxygen, nitrogen, etc.) in an exhaust gas.    [Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 64-41184
3. Problems to be Solved by the Invention
However, in Patent Document 1, a lubricant must be applied to a sliding face of a crimper at every crimping operation, which complicates the manufacturing process of the crimp contact. Further, the lubricant tends to adhere to outer surfaces of both side portions of a hold portion. This is because the lubricant is applied in advance to a sliding face of the crimper. When a gas sensor having such a crimp contact is used as an oxygen sensor mounted on, for example, an engine exhaust pipe or the like, the temperature of the hold portion of the crimp contact becomes considerably high. As a result, the lubricant, which adheres to the outer surfaces of the side portions of the hold portion, is thermally decomposed and generates a decomposition gas. Further, the thus-produced decomposition gas causes a fluctuation in the electromotive voltage of the gas sensor, thereby resulting in a measurement error. Furthermore, the specification of Patent Document 1 discloses that a lubricant (e.g., tetrafluoroethylene, carbon or the like), which does not generate a decomposition gas, is preferably selected for a crimp contact provided in an oxygen sensor or the like. However, it is troublesome to select a type of lubricant according to the environment where the gas sensor is to be used.